A natural or synthetic crystalline micro-porous molecular sieve has been demonstrated to have catalytic properties for various types of hydrocarbon conversion processes. In addition, the crystalline micro-porous molecular sieve has been used as adsorbents and catalyst carriers for various types of hydrocarbon conversion processes and for other purposes. The molecular sieve is a regular porous crystalline material having a limited crystalline structure when measured by X-ray diffraction, and has many small hollows therein, which can be connected to one another by smaller channels or pores. The channels or pores have about the size to allow adsorption of molecules in a specific size while refusing molecules in a large size. An interstitial space or a channel formed by the crystalline network structure enables a molecular sieve such as crystalline silicate, aluminosilicate, crystalline silicoalumino phosphate and crystalline aluminophosphate to be used as a molecular sieve for a separation process and as a catalyst and a catalyst support for a wide variety of hydrocarbon conversion processes.
Within the pores of the crystalline molecular sieve, hydrocarbon conversion reactions such as an isomerization reaction of paraffin, an isomerization reaction of olefin skeleton or double bonding, a disproportionation reaction, an alkylation reaction and a transalkylation reaction of an aromatic compound are controlled by a binding force granted by the channel size of the molecular sieve. Where a fraction of a feedstock is overly large so that it cannot be introduced into and reacted in pores, a problem of reactant selectivity occurs. Where a part of a product cannot leave channels or does not subsequently react, a problem of product selectivity occurs. Product distribution may vary depending on transition state selectivity, and this is because the reaction transition state is so large that it cannot be formed within the pores, and thus, a certain reaction cannot occur. In addition, where a size of the molecules is approximate to a size of the pore system, the problem of the selectivity may be caused from the structural binding to diffusion. A non-selective reaction on a molecular sieve surface, e.g., a non-selective reaction on an acid site of a molecule sieve surface, is not generally desirable, because the reaction is not applied to shape selective binding granted to a reaction occurring within channels of the molecular sieve.
Zeolite is a crystalline micro-porous molecular sieve formed of lattice silica and/or alternatively alumina, which is bounded to a replaceable cation (e.g., an alkali metal or alkali earth metal ion). The term “zeolite” includes a material containing silica and alternatively alumina, but parts of the silica and the alumina are recognized to be wholly or partially substitutable with different oxides. For example, germanium oxide, titanium oxide, tin oxide, phosphorous pen oxide and a mixture thereof may substitute a part of the silica. Boron oxide, iron oxide, gallium oxide, indium oxide and a mixture thereof may substitute a part of the alumina. Accordingly, the terms “zeolite,” “zeolites” and “zeolite material” used herein mean not only a material containing a silicon atom and alternatively an aluminum atom within its crystalline lattice structure, but also a material containing substitution elements suitable for the silicon and the aluminum, e.g., gallosilicate, borosilicate, silicoaluminophosphate (SAPO) and aluminophosphate (ALPO). The terms “aluminosilicate zeolite” used herein mean a zeolite material essentially containing a silicon atom and an aluminum atom within its crystalline lattice structure.
In a certain hydrocarbon conversion process, it is sometimes preferable to reform a catalyst used in the process to maximize performance of the catalyst in the certain hydrocarbon conversion process [Korean Patent Application Publication No. 10-2002-0010143, etc.].
For example, it is sometimes preferable that a catalyst used in a hydrocarbon conversion process is a multi-functional catalyst, for example, a tri-functional catalyst or a bi-functional catalyst. The bi-functional catalyst includes two species of individual catalysts, e.g., two species of zeolites having different compositions or structures for inducing individual reactions. A reaction product may be separate, or two species of catalysts may be used together such that a reaction product of one catalyst may be carried on a catalytic site of a second catalyst to be reacted thereon. In addition, one of advantages in using the zeolite catalyst is that the catalyst is shape selective, and a non-selective reaction on a zeolite surface is not generally preferable. Thus, it is sometimes preferable that a catalyst used in a hydrocarbon conversion process has an ability to prevent or at least reduce an inappropriate reaction that may occur on the surface of the zoelite catalyst, by selectively selecting molecules within a supply stream based on their sizes or shapes so as to prevent inappropriate molecules existing in the supply stream from entering onto the zeolite catalyst and reacting with the catalyst. Furthermore, the performance of the zeolite catalyst may be sometimes maximized where the catalyst selectively selects target molecules based on their sizes or shapes to prevent the molecules from being out of the catalyst.
However, when conventional Al-containing zeolite is used as a catalyst for a hydrocarbon conversion reaction, there is a problem in that Al is eluted from the zeolite thereby deteriorating the hydrocarbon reaction. Thus, development of a zeolite structure that can resolve the problem is being demanded.